Wastewater treatment process

ABSTRACT

A process for treating wastewater containing insoluble solid waste material and soluble solid waste material including the following series of steps: (1) controlling the oxygen content of the wastewater to a level at which growth of anaerobic bacteria is substantially eliminated, (2) separating the insoluble solid waste material from the wastewater, (3) treating the soluble solid material in the wastewater with a predetermined amount of aerobic bacteria, and (4) reducing the amount of aerobic bacteria in the wastewater. The insoluble solid waste material separated from the wastewater can be burned to produce electrical energy. Apparatus for carrying out the process are also disclosed.

BACKGROUND OF THE INVENTION

For the entire history of the treatment of waste products produced bythe bodies of animals or mankind, a naturally occurring process has beenthe basis for the treatment of carbon-based and other compounds thatmake up the body waste. The presence of several types of bacteria whichare included in the waste body products from all animals and mankindhave provided the means of treatment by either of two biologicalprocesses. One class of naturally occurring bacteria utilizes anydissolved oxygen in the water phase of the waste to oxidize the wasteproducts with the resulting production of water, carbon dioxide andother oxide products. If the waste liquid phase does not containdissolved oxygen, the second class of naturally occurring bacteria isable to act on the carbon-based and other compounds with the resultingproduction of hydrogen sulfide, methane and other complex organiccompounds.

The general classification for the bacteria that require dissolvedoxygen in the liquid phase of the waste water for growth is aerobicbacteria. Due to the very low solubility of oxygen in water, air must bein contact with the wastewater on a frequent cycle basis in order toresupply the dissolved oxygen in the wastewater. The second naturallyoccurring general class of bacteria is anaerobic bacteria which is basedon the requirement that there cannot be any amount of dissolved oxygenin the wastewater for its growth to occur.

As the by-products produced by the aerobic bacteria growth in wastewaterdo not present a danger or provide an unacceptable secondary problem tomankind, it has in almost all cases become the primary process forwastewater treatment. The planned use of the second naturally availablebacteria, anaerobic, has been confined to situations that lendthemselves to the use of closed tanks or underground containers. Theby-products produced by the action of the anaerobic bacteria result inmajor problems in the area of explosion hazard, corrosion problems,offensive odor and toxic reaction to mankind. The past and currentprocesses for the treatment of wastewater are based on the use of thenaturally occurring bacteria in either the aerobic bacterial cycle orthe anaerobic bacterial cycle with the design of the treatment systembeing controlled by the ability to provide the most efficientenvironment for either type of bacterial growth. This design factor hasto also have as a major consideration the disposal of the by-products ofthe bacterial action.

The treatment of wastewater does not begin at the treatment plant andthis factor has become a major problem as the size of collection andtransmission systems have been increased to minimize the number oftreatment plants required. The action of the naturally occurringbacteria begins at the point of introduction of the body waste productsinto a water carrier. The growth of the aerobic bacteria is normally thefirst action as most wastewater liquid phases will contain some amountof dissolved oxygen. If the dissolved oxygen level is not maintained atsome positive value, the growth of the aerobic bacteria will stop and bereplaced by the growth of dormant anaerobic bacteria. The action of theaerobic bacteria is a self-limiting factor based on the availability ofdissolved oxygen in the liquid phase. The lower the concentration ofdissolved oxygen in the liquid phase, the slower the growth rate of theaerobic bacteria. Increases in the retention time in the collection andtransmission systems associated with the treatment plant affects thecondition of the wastewater received and the treatment process used.Without the wastewater being exposed to air contact, the loss ofdissolved oxygen concentration can result in wastewater being receivedat the treatment plant in a condition that can adversely affect thenormally used aerobic process.

Since a means for effectively controlling dissolved oxygen levels to asufficient level in the collection and transmission systems was notpreviously available, the final treatment process was limited to thecontinuation of the process provided by natural occurrence. Only theselection of the type of aerobic or anaerobic process to continue thebiological treatment could be utilized in wastewater treatment plants.

Three types of aerobic biological treatment processes are the mostcommonly found in wastewater treatment plants: the extended aerationprocess, the contact stabilization process and the complete mix process.All three processes utilize aeration devices to increase the dissolvedoxygen concentration of the liquid phase of the wastewater and thereturn of wastewater solids with high concentrations of bacteria growth.The main differences between the three processes is the amount ofretention time of the wastewater in the aeration zones of the treatmentprocess, the amount of return of wastewater solids with high bacterialgrowth and the amount of wastewater solids that remain to be disposed ofafter the aeration process. The problem of disposal of the excesswastewater solids or sludge resulting from any of the three biologicaltreatment processes has become a major threat to not only mankind, butalso to the entire planet by destruction of the water supply necessaryfor both animal and human life. The amount of sludge generated by thethree different biological processes is generally in the same ratio asthe amount of retention time utilized in the aeration zones of thetreatment process. For all three of the processes used, secondarytreatment of sludge by either aerobic or anaerobic bacterial action isrequired The greater the amounts of sludge developed by the shortretention times in the aeration zones of the treatment process, thegreater the production of hazardous sludge that will require secondarytreatment and controlled disposal.

The development of the centrifugal oxygenator described in U.S. patentapplication Ser. No. 07/109,192 filed Oct. 16, 1987 (which is acontinuation of U.S. patent application Ser. No. 06/799,104 filed Nov.18, 1985, now abandoned) and pending PCT application PCT/US86/02542, thecontents of each of which are incorporated herein by reference, nowprovides the means to control the dissolved oxygen levels in wastewatercollection and transmission systems which, in turn, allows the controlof the naturally occurring bacterial growth. The centrifugal oxygenatorhas prove by certified testing that it has the ability to provide oxygentransfer rates of 40% in liquid levels of only two feet to as high as98% at liquid levels of over twenty feet. Unlike prior aeration devices,the centrifugal oxygenator provides complete control of the air or gasflow rate from 0% to the maximum capacity of the unit size. Thecentrifugal oxygenator can operate on a stop/start basis without anyclogging of the air or gas flow passages and also provides a highvelocity directionalized mixing and solid suspension hydraulic flow fromthe unit

SUMMARY OF THE INVENTION

The present invention provides a process for treating wastewatercontaining insoluble solid waste material and soluble solid wastematerial comprising the following series of steps: controlling theoxygen content of the wastewater to a level at which growth of anaerobicbacteria is substantially eliminated, separating the insoluble solidwaste material from the wastewater, treating the soluble solid materialin the wastewater with a predetermined amount of aerobic bacteria andreducing the amount of aerobic bacteria in the wastewater, and alsoprovides an apparatus for its practice.

The present invention combines the purification of wastewater with thedisposal of waste paper materials for the generation of electricalpower. The process does not rely on either aerobic or anaerobic bacteriafor chemical modification of the non-soluble wastewater solids.Biological treatment is confined to the soluble material in thewastewater. The process utilizes control of dissolved oxygen levels inthe wastewater collection, transmission and treatment system in place ofthe currently applied uncontrollable addition of air or other oxidizingchemicals. Previous means for addition of air to wastewater were limitedin their ability to operate under the conditions of start/stop orvariable gas rate requirements needed for the control of dissolvedoxygen levels. The use of centrifugal oxygenators provides the means ofcontrol of the dissolved oxygen in wetwells, pipelines and throughoutthe wastewater treatment plant, thus providing the means for control orelimination of the growth of anaerobic bacteria and minimizing thegrowth of aerobic bacteria. With the placement of centrifugaloxygenators in gravity collection manholes and pump station wetwells ofadequate size to provide sufficient retention time for oxygen transfer,and as sidestream circulators in force main transmission pipelines usingpure oxygen gas feed to the centrifugal oxygenator, control of dissolvedoxygen levels is possible with the result that the control of bothanaerobic and aerobic bacterial development is now possible.

The efficiency of both physical separation of the wastewater solids andthe recovery of the energy value of the solids are a function of theelimination of the growth of anaerobic bacteria in the collection andtransmission systems and the minimizing of the growth of aerobicbacteria by the maintenance of minimum levels of dissolved oxygen in thecollection and transmission portions of wastewater systems. Wastewatertransmission systems can now be designed on either a constant rate orconstant pressure basis using the control of dissolved oxygen in storagetype wetwells in primary and repump stations and pipeline injection ofpure oxygen. Either of these designs will greatly reduce the storagerequirement at the treatment plant necessary for the constant rateoperation of the plant process.

With the means for controlling the dissolved oxygen levels, which inturn minimizes the bacterial growth, and the additional means ofproviding the constant flow rates in the wastewater treatment process,two additional problems must be solved to provide high efficiencyseparation by air flotation. The control of the raise rate of the airbubble must be maintained as close as possible to the physicallimitations imposed by the difference in specific gravity of the gas andliquid phases. This is accomplished by dispersion of the gas phase intovery small size gas particles and the use of positive gas pressure abovethe surface of the liquid phase. To further increase the separationefficiency, fibrous material is contacted with the wastewater solidsprior to introduction into the pressurized separation column. The lowdensity fibrous material attachment to the wastewater solids providesassistance in the flotation separation in two ways. The primaryassistance is the high degree of attachment of the air bubble to theirregular surface of the fiber, and the second is the decrease in thedensity of the wastewater solid by its attachment to the low densityfiber. These actions greatly increase the separation efficiency of theflotation process.

The primary step for the separation of the waste-water solids from itsliquid carrier is a two-stage pressurized air flotation system using theaddition of a fiber slurry prepared from waste paper material toincrease the physical separation efficiency of the flotation process.The second step applies batch/continuous aerobic biological action forthe treatment of soluble matter. The third step uses high liquid level,high efficiency solids removal settling to remove solids not removed inthe primary step. The final step in the wastewater treatment processapplies contact columns with coal and paper fiber media for solidsremoval and bacterial reduction. The soluble material in the wastewateris treated by controlled aerobic biological action in batch/continuousvariable operating level aeration tanks with the controlled addition ofreturn activated sludge which has a known concentration of dissolvedoxygen and a known concentration of aerobic bacteria. The level ofdissolved oxygen in the batch/continuous aeration tanks can becontrolled at minimum required levels for the treatment of the solublematerial in order to minimize the amount of bacterial growth on thewastewater solids not removed by the pressurized air separation phase ofthe treatment process. The high efficiency settling tanks (clarifiers)obtain their increased efficiency as compared with current designs by asubstantial increase in the liquid level which is allowable by theremoval of most of the wastewater solids in the primary stage, thecontrol of bacterial concentrations and the control of the dissolvedoxygen levels in the feed to the settling tanks. The contact columns actas a final removal stage for all wastewater solids and also thereduction in bacteria in the effluent of the treatment process usingprecontact column chlorination. The contact columns contain single use(one operating cycle) mixed media of coal particles and paper fiber. Inaddition to the mixed media, a high concentration of chlorine orsimilar-acting chemical is maintained in the contact columns for highefficiency bacteria reduction.

The wastewater solids are combined with the coal and paper fibermaterials and thereafter used as a fuel for the energy recovery powergeneration section of the treatment plant. The process utilizes aninternal reuse effluent system to supply cooling water to the condenserof the power plant system and other needs in the process for mediapreparation, transfer and energy recovery. An internal reuse storage andchlorine contact tank equipped with a centrifugal oxygenator is used toremove any excess chlorine from the reuse effluent by air strippingusing the fine bubble dispersion and increased oxygen levels which canbe provided by the centrifugal oxygenator. After internal reuse, theeffluent is treated for any needed adjustment in the dissolved oxygenconcentration by use of centrifugal oxygenators with enriched or pureoxygen supplied in either a liquid or gas phase from bulk storage tanksor cylinders. All wastewater solids that are removed and the fibermaterial and coal added for the operation of the process of the presentinvention are mixed with the additional coal and shredded paper wasteand used as fuel for the power generating system incorporated in theprocess design, thus completely eliminating the need for disposal oradditional treatment of the partially treated wastewater solids, thusproducing a sludge-free process.

The process reduces the requirement for the return of activated sludgeby an average factor of ten, thus greatly reducing the internal flowrequirement of the treatment plant. The internal flow is also reduced bythe elimination of the recycle wash water needed for many type offilters used for final effluent quality control. The process provides asuperior effluent quality by the use of a nonbackwash single use (oneoperating cycle) high efficiency dual mixed media of solids and fiber inthe contact columns for solids removal and bacterial reduction in placeof tertiary filters or similar types of solids removal devices thatrequire backwash water for removal of the trapped solids. The use of aconstant pressure and/or a constant rate design system in the collectionand transmission sections of the wastewater system can provide aneffective and low-cost reduction in the wastewater storage requirementand the treatment needed for the operation at a constant rate. In orderto provide control of dissolved oxygen levels in the collection andtransmission systems, pump station wetwells must be increased in size ascompared to current design practice. By increasing the pump stationwetwell size above that needed for dissolved oxygen control, storagecapacity for either the constant pressure or constant rate transmissionsystem can be obtained at very small increases in initial cost.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a flow diagram through the major components ofequipment of the present invention. Secondary items such as controlvalves, isolation valves, electrical supply and control equipment arenot shown in FIG. 1.

FIG. 2 is a side elevational view, partially in section, of an airdispersion column which may be used in the present invention. FIGS. 2A,2B and 2C are top cross-sectional views of the air dispersion column ofFIG. 2 along lines 2A--2A, 2B--2B and 2C--2C, respectively.

FIG. 3 is a side elevational view, partially in section, of apressurized air separation column which may be used in the presentinvention. FIGS. 3A and 3B are top cross-sectional views of thepressurized air separation column of FIG. 3 along lines 3A--3A and3B--3B, respectively.

FIG. 4 is a side cross-sectional view of a clarifier or settling tankincluding a coil track conveyor which may be used in the presentinvention. FIGS. 4A and 4B are top cross-sectional views of theclarifier or settling tank of FIG. 4 along lines 4A--4A and 4B--4B,respectively.

FIG. 5 is a side elevational view, partially in section, of a contactcolumn which may be used in the present invention.

FIG. 6 is a side cross-sectional view of a chlorine contact and reusestorage tank which may be used in the present invention. FIG. 6A is aplan view of the chlorine contact and reuse storage tank of FIG. 6 alongline 6A--6A.

FIG. 7 is a side cross-sectional view of a concentration column whichmay be used in the present invention. FIG. 7A is a plan view of theconcentration column of FIG. 7 along line 7A--7A.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The treatment of wastewater does not begin at the treatment plant.According to the present invention, the wastewater, specifically thebacteria therein, is controlled in the collection and transmissionsystem. The oxygen content is controlled to a level such that the growthof anaerobic bacteria is substantially eliminated and the growth ofaerobic bacteria is minimized. The oxygen content is controlled by useof, inter alia, centrifugal oxygenators, of the type described in U.S.patent application Ser. No. 07/109,192 and PCT application No.PCT/US86/02542.

The level of dissolved oxygen needed in both the collection andtransmission system is a function of the initial concentration of boththe aerobic bacteria and the retention time required before additionaloxygen can be added to the wastewater. For example, for low levels ofaerobic bacteria and low retention times, dissolved oxygen levels offrom 0.1 to 0.3 ppm could be sufficient to maintain a positive level ofdissolved oxygen throughout the complete retention time until additionaloxygen could be added. In other systems, the concentration of aerobicbacteria could be naturally higher caused by water with high levels ofdissolved oxygen. Such systems, with longer retention times untiladditional oxygen could be added, would require dissolved oxygen levelsof 2.0 to 3.0 ppm to store sufficient oxygen in the liquid phase toprevent the complete destruction of the aerobic bacteria and to preventthe growth of anaerobic bacteria until additional oxygen could be added.

The need to maintain a low level of positive dissolved oxygenconcentrations in all of the different systems that have variations inretention time, aerobic bacteria concentrations and dissolved oxygenlevels, requires variable levels of dissolved oxygen in each collection,transmission and treatment system. The efficiency of the physicalseparation process is a function of the amount of bacterial developmenton the wastewater solids which, in turn, is controlled by maintainingthe lowest possible positive dissolved oxygen levels in the collection,transmission and storage systems.

The ability to control bacterial growth in wastewater collection andtransmission systems by the development of the centrifugal oxygenatorallows for the application of a process system for the separation ofhigh energy solids, with combustion values similar to coal, from thewater carrier even with a solids concentration of only 0.1 to 0.2%. Tocomplete the purification of the wastewater, a biological process mustbe combined with the solids separation process for the removal of thesoluble organic matter in wastewater that cannot be removed by thesolids separation process.

Another factor for the efficient separation of the low percentage solidsis the operation of the treatment process at a constant flow rate. Allcurrently used treatment processes must operate with flow rates thatvary from as much as 250% increase over average daily flow during peakperiods to as low as 10% of average daily flow during night and earlymorning periods. With the development of the centrifugal oxygenatorwhich can efficiently operate at liquid levels of from two feet to 100feet, it is possible to provide storage of wastewater in excess of theaverage daily flow at the treatment plant. To improve the efficiency ofthe present invention, a certain amount of wastewater storage at thetreatment plant can be provided for dissolved oxygen control. Further,modification of the current design standards for collection andtransmission systems can obtain the best cost efficiency as comparedwith treatment plant storage.

The current design practice for pump station wetwells in wastewatercollection and transmission systems o necessity have to be confined tothe smallest possible retention volume of the wastewater for the flowconditions. This restriction is imposed by the settling of solids in thewetwell and the inability to control dissolved oxygen levels in thewetwell. With the availability of the centrifugal oxygenator, it ispossible to totally remove this design restriction. Wetwells can nowbecome a storage facility for wastewater flow in excess of the averagedaily flow. In order to control the dissolved oxygen levels in thecollection and transmission systems, retention times in pump stationwetwells are the least costly method of providing the time required forthe controlled transfer of dissolved oxygen into the wastewater. As thecentrifugal oxygenator provides both efficient transfer of oxygen aswell as hydraulic flow velocity at its directionalized discharge,settling of wastewater solids in the wetwells is no longer aconsideration in the design of wetwells of pumping stations Waste-watercollection and transmission systems pump station wetwells when equippedwith centrifugal oxygenators, which do not affect the operation ofcentrifugal pumping equipment, can now be designed to provide anretention time for the wastewater that is the most efficient for systemflow requirements that vary from system to system. As long as theretention time needed for flow control exceeds the retention time neededfor dissolved oxygen control, sizing of the storage wetwell would bedetermined by the systems' flow requirements. This method of meeting theconstant flow requirement of the energy recovery sludge free wastewatertreatment process of the present invention provides a second majorbenefit by increasing the capacity of existing transmission pipelinesand reducing the size requirement and cost of future pipeline systems.In addition, the energy recovery sludge free wastewater treatmentprocess disclosed herein eliminates the requirement for variable speedpump drives and reduces the electrical power consumption of anywastewater system.

As all wastewater transmission pipeline systems are currently designedfor handling the peak flow requirement of over 200% of average dailyflow, retention time in the pipeline can result in the development ofdangerous problems in the pipeline system. During peak flow periods,most pipeline systems are designed so that the retention time isinadequate to allow the depletion of the dissolved oxygen levels in thewastewater by bacterial action. During the period of average daily flow,the retention time is at least doubled and during night time or earlymorning periods, the retention time in pipeline systems can be increasedby a factor of 10 to 20 times which, in some cases, results in extensiveproblems of explosion hazard, corrosion of concrete and metalcomponents, foul odor, toxic health hazards and treatment plantoperational problems.

With a method for the control of bacterial growth in wastewatercollection and transmission systems and the ability to operate thetreatment process at a constant flow rate, the efficiency of thephysical separation of the solids from the water carrier and thepreservation of the combustion valve of the solids, coupled with thetreatment of the soluble organic matter, makes the energy recoverysludge free process described herein possible. This process combines theseparation of solids by both fiber assisted pressurized air flotation;settling using a high liquid level depth which is normally double thoseused in all current processes; and a solids collection and removalsystem that uses a concentric circular flow pattern in place of apusher-type rake system for moving the settled solids to a central pointof discharge. The multiple process requirement is needed due to thevariation in wastewater from system to system and efficient operation ofthe overall treatment process.

For the efficient separation of the solids from the liquid phase ofwastewater by the energy recovery sludge free process, the growth ofboth aerobic and anaerobic bacteria must be controlled in the wastewatercollection and transmission systems. Also, for efficient separation ofthe solids from the liquid phase, it is necessary to operate thetreatment plant at a uniform flow rate. Current treatment processes areoperated without control of bacteria growth and at variable flow ratesthat can have as much as a 25 time variation in the input flow from thecollection and transmission systems.

The only means of non-destructive control of bacteria growth is the useof the control of dissolved oxygen in the collection and transmissionsystems. This control of dissolved oxygen eliminates the growth ofanaerobic bacteria and minimizes the growth of aerobic bacteria bylimiting the amount of dissolved oxygen available for growth.

In order to control dissolved oxygen in the collection and thetransmission systems, retention time for the transfer of oxygen into thewastewater must be provided within these systems by the use of oversizewetwells for pump stations and the injection of oxygen in long retentionpipeline systems.

This requirement is compatible with the requirement for the constantflow rate needed for efficient operation of the separation stages of theenergy recovery sludge free treatment process. Using centrifugaloxygenators in pump station wetwells for dissolved oxygen control alsoallows the size of the wetwells of pump stations to be increased forstorage of peak flow that always occurs in collection systems.

Using the storage of peak flows in collection systems, it is possible togreatly decrease the amount of storage needed at the treatment plant forefficient operation. At the same time, the use of storage wetwellsprovides a great amount of cost savings and a reduction in operatingproblems when compared to the currently used inflow demand systems.

The constant rate transmission system eliminates the design constraintsof the inflow demand system which requires the output of the pumpstation to generally match the variable inflow of the pump station. Withuse of constant speed pumps operating on a selectable time basis withthe excess incoming flow stored in the wetwell, control of dissolvedoxygen and a nearly constant rate of flow can be delivered to thetreatment plant.

The constant pressure transmission system is similar to the constantrate transmission system in that it also uses storage type pump stationwetwells for dissolved oxygen control and storage of excess incomingflows. This system would be used in some cases where it is not possibleto provide a large enough wetwell for the incoming flow storage. Thetransmission system that would require the constant pressuretransmission design would have a mixture of constant speed pumps andvariable speed pumps. The constant speed pump stations would be operatedin the same manner as in the constant rate system and the variable speedpumping station would have its pump speed, and therefor its output,controlled by the placement of the normally used transducer speedcontrol sensor operated based on the pressure in the force main in placeof the liquid level in the wetwell. This constant pressure systemprovides the same constant flow rate to the treatment plant with thesame operating cost savings as the constant rate system.

FIG. 1 shows a preferred treatment flow diagram for wastewater which hasbeen controlled in the transmission and collection system as previouslydescribed.

As shown in FIG. 1, an in-line grinder/comminutor 1 is provided for thereduction of large size solids in the wastewater to a more suitable sizefor the physical separation process. The wastewater then flows toconstant rate feed and dissolved oxygen control tanks 2.

Constant rate feed and dissolved oxygen control tanks 2 have a dualfunction of storing excess flow into the wastewater treatment plant andstabilizing the dissolved oxygen concentration at an appropriate levelas explained above such that the growth of anaerobic bacteria issubstantially eliminated and the growth of aerobic bacteria isminimized. In an average case, the level of dissolved oxygen may bebetween 0.5 and 1.0 parts per million (ppm). For most efficientoperation, the treatment process is operated at a constant flow rate andthe sizing of the tank capacities are based on the design of thecollection and transmission systems and the ability to provide constantflow rates to the treatment plant. The use of a constant pressure or aconstant rate design system in the transmission section supplying thewastewater treatment plant as previously described will minimize thesize of the constant rate feed and dissolved oxygen control tanks 2.

Centrifugal oxygenators 3 are installed in the constant rate feed anddissolved oxygen control tanks 2 for the dual purpose of suspendingsolids by hydraulic flow and controlling the dissolved oxygen levels.Based on the ability of the centrifugal oxygenator 3 to provide highefficiency oxygen transfer at any liquid level above the two footminimum level, the constant rate feed and dissolved oxygen control tanks2 can be operated at any variable liquid level in excess of two feet toas much as fifty feet. The centrifugal oxygenator 3 is able to operateat any gas flow rate from zero to the maximum for the size unit usedwithout any type of plugging. The centrifugal oxygenator 3 also providesfor start/stop gas flow for control of the dissolved oxygen level in theconstant rate feed and dissolved oxygen control tanks 2 withoutaffecting the hydraulic suspension of the wastewater solids.

A solids handling type of centrifugal pump 4 is used to transfer thewastewater from the constant rate feed and dissolved oxygen controltanks 2 to the first stage air dispersion column 5. Due to the variableheight of the wastewater in the constant rate feed and dissolved oxygencontrol tank 2 and a constant injection pressure required by the firststage air dispersion column 5, the centrifugal pump 4 must utilizeeither a flow control valve system or a variable speed drive system.Downstream of the centrifugal pump control valve, a pipeline injectpoint is located prior to the first stage air dispersion column 5 entrypoint. Fiber slurry produced by the paper to fiber with high shear mixer45 is injected into the pipeline by the fiber slurry transfer pump 67for contact with the wastewater solids. The fiber particles, due totheir surface nature, attach themselves to the wastewater solidparticles and thereby increase the separation efficiency of thepressurized air separation columns 7 and 10. To accomplish this, air isdispersed in the wastewater in first and second stage air dispersioncolumns 5 and 8, equipped with air dispersers 6 and 9, respectively.

In particular, as shown in FIGS. 2, 2A, 2B and 2C, the first stage airdispersion column 5 is a vertical pressurized unit with the interior ofthe column 5 divided into a minimum of two sections 508 and 516. Theflow from the centrifugal pump 4 is introduced into the lowest sectionof the column 5 near the bottom of the section, but above the airdistributor plate 502 through inlet 506. The bottom column head 522contains the air supply inlet flange 524 which provides the air supplybelow the air distributor plate 502. The air distributor plate 502provides for the introduction of the compressed air in a uniform mannerthrough holes 503 to the incoming wastewater. The lowest section 508 ofthe column 5 is separated from the second stage 516 and any additionalstages by a horizontal baffle 512 which provides the dual function offlow pattern control for efficient gas dispersion and directing the flowof the first stage 508 into the center of the column 5 to allow completecontact with the second stage air dispersion impeller 606. The firstdispersion stage 508 of the column 5 has near its bottom the airdistributor plate 502 which directs the flow of air into the center ofthe column 5 in order to allow complete contact with the first stage airdisperser impeller 614. Both the first dispersion stage 508 and thesecond dispersion stage 516 contain vertical baffles 510 to improve thedispersion of the air into the wastewater. The second dispersion stage516 has a horizontal baffle 504 to improve the flow pattern andefficiency of the second stage air dispersion impeller 606. The secondstage air dispersion column 8 can be of similar construction to thefirst stag air dispersion column 5 and, if required, additional stagescould be used in the design of either air dispersion column 5 or 8 toobtain suitable air dispersion in the wastewater. The air disperserdrive 602 drives shaft 603 and impellers 606 and 614, and would besimilar for both the first stage air dispersion column 5 and the secondstage air dispersion column 8. The air pressure within the dispersioncolumn 5 is controlled by the use of a pressure relief valve 518 placedin the top head of the column 5. The wastewater air dispersion isdischarged from the column 5 near the top head 520 of the column 5,i.e., just below horizontal baffle 504 through outlet 521. The top head520 of the column 5 would have a flange-type mounting for the firststage air disperser unit.

The first stage air disperser 6 is an electric drive high shearmulti-stage rotating impeller unit with the impellers 606 and 614designed for dispersion of the air into the wastewater flow. Theimpellers are selected from the maximum required air flow rate which, inturn, must be determined by (1) the concentration of the solids in thewastewater, (2) the amount of fiber slurry added to the wastewater, (3)the vertical liquid flow velocity in the column, (4) the level of backpressure required for control of the air bubble rise rate, and (5) thevolume of air required for efficient flotation separation of thewastewater solids.

Referring back to FIG. 1, the second stage pressurized air dispersioncolumn 8 would be the same design as the first stage pressurized airdispersion column 5, but in the average case, somewhat smaller indiameter and designed for lower air flow rates.

The second stage air disperser 9 would also be similar to the firststage air disperser 6, but in the average case, a smaller electric motordrive could be used.

The pressurized air flotation utilizes a two-stage system of verticalcolumns 7 and 10 with compressed air dispersed in units 5 and 8 asdescribed prior to the introduction of the wastewater and the airdispersion near the bottom of the columns. The vertical height and theinternal flow patterns within the columns 7 and 10 must be determined bythe composition of the wastewater solids. In general, the pressurizationof the first stage column 7 will be higher than the second stage column10 because the vertical rise rate of the air bubble is a function of theamount of pressure above that of the normal atmosphere pressure at thelocation of the treatment plant.

The ability of separation of low solids concentrations in a water phaseby the air flotation process requires the attachment of the rising airbubble to a solid particle with control of the rise rate to a low enoughlevel to maintain contact with the solid particle. Since the liquidlevel in the column can vary based on the composition of the solids inthe wastewater, the control of the air pressure above atmosphericpressure above the top of the liquid level in the column can be adjustedfor maximum solid separation efficiency. The second stage pressurizedair separation column 10 would utilize a smaller diameter for almost thesame liquid flow that would result in a greater vertical rise velocityof the liquid and solid phase and a lower pressurization that wouldincrease the rise rate of the air that was introduced by a second stageair dispersion unit 8, 9 that would receive the flow from the firststage separation column 7. The first stage pressurized air separationcolumn would be selected and designed for smaller size particles usinghigher rates of liquid and air bubble rise rates. The solids separatedat the upper level of both the first and second stage columns 7 and 10would be withdrawn by use of a control valve and discharged from thecolumns using the internal pressure of the column. Any solid materialwith a high settling rate would be collected in the bottom of both thefirst and second stage columns 7 and 10 and discharged by a controlvalve utilizing the pressurization of the columns to a secondaryconcentration column 48.

The internal flow pattern of both the first and second stage separationcolumns 7 and 10 utilizes a circulating horizontal directionalized flowof the wastewater and air dispersion. The bottom stage of both columnsallows the flow to either travel downwardly into the high density solidsremoval stage or upwardly into the first flotation stage of the columns.Additional flotation stages are stacked above the first flotation stage,but these stages have a flow pattern somewhat different from the firststage. The vertical travel flow path would be the same as the firststage, but a second flow pattern would be used for the separated liquidphase. The liquid flow would utilize a horizontal slotted openinglocated directly above the horizontal stage separation baffle that woulddischarge into a vertical closed pipe or formed section of the column toremove the separated liquid phase, as described hereinafter.

The first stage pressurized air separation column 7 (shown in moredetail in FIGS. 3, 3A and 3B) has a vertical two section design with theinflow of the wastewater an air dispersion introduced into the columnsettling section 730 by way of the circular ring inlet manifold 724 andthe opposed liquid velocity inlet nozzles 726. By utilizing an opposedliquid velocity inlet design of the nozzles 726, the velocity head ofthe liquid is dissipated and a low velocity circular flow pattern iscreated in the center of the column 7. In the low velocity circular flowpattern of the center of the column 7, high density solids (grit andother inorganic solids) settle to the bottom of the column bottom head704 and are discharged under column pressure through the high densitysolids discharge 706 by use of an exterior control valve. The lightdensity solids and waster phase rise vertically in the low velocitycircular flow pattern of the column settling section 730 and aredischarged into the column flotation section 728 which is divided fromthe column settling section 730 by the column divider plate 718. Thelight density solids and the water phase are introduced into the columnflotation section 728 using the low density solids and waterdirectionalized inlet distribution 720 and the baffle fordirectionalized flow 722. The low density solids and water phase travelin a circular vertical rise pattern over the fixed vertical flight lightdensity solids conveyor 716. The center of the fixed vertical flightlight density solids conveyor 716 is a circular enclosed pipe sectionwhich forms the separated water discharge pipe 712. Water is separatedfrom the light density solids using inlet openings 714 located in theseparated water discharge pipe 712 at a position just above the pointsof flight where the light density solids conveyor 716 comes in contactwith the separated water discharge pipe. The collector discharge waterflow inlet openings 14 of the separated water discharge pipe 712 allowthe discharge of the separated water through the top head 702 by theseparated water discharge outlet 710. The fixed vertical flight lightdensity solids conveyor 716 allows the light density solids to collectunder the top head 702 between the outer wall of the column and theseparated water discharge pipe 712 where they are discharged under thecolumn operating pressure through the light density solids dischargeoutlet 708 using an exterior control valve.

Referring back to FIG. 1, the second stage pressurized air separationcolumn 10 would be similar in design to the first stage pressurized airseparation column 7, but in the average case, somewhat smaller indiameter and with the internal pressure controlled at a lower level thanthe first stage pressurized air separation column 7 for control of boththe air bubble rise rate and the vertical liquid velocity.

The floatable solids from the top stage of both the first and secondstage separation columns 7 and 10 would be discharged under pressure bya control valve and transferred to the slurry mixing tank 42 for mixingwith other flow streams prior to dewatering.

The high density solids collected in the bottom stage of both the firstand second stage pressurized air separation columns 7 and 10 would bedischarged under pressure by control valves to a secondary concentrationcolumn 48.

The concentration column 48 would also be a pressurized stage with theunderflow discharged into the same slurry tank 42 as the solids from thetop flotation stage of the first and second stage separation columns 7and 10. The overflow of the concentration column 48 would be dischargedinto the constant rate feed and dissolved oxygen control tank 2.

After the separation of both the floatable solids and the high densitysettleable solids from the two-stage pressurized air separation columns7 and 10, the wastewater would be discharged under pressure to a seriesof batch/continuous aeration tanks 11 with operating liquid levels of aminimum of twenty feet or up to fifty feet depending on the liquid levelof the pressurized air separation columns 7 and 10 and their operatingpressure. As one of the aeration tanks 11 is being filled by the flowfrom the separation columns 7 and 10, other tanks 11 are used forbacterial oxidation of the soluble organic material or for providing theconstant rate feed to the settling tanks 17 of the invention.

By eliminating variations in flow rates and the inaccuracy of acontinuous flow-through system, accurate control of the bacteria actionby control of dissolved oxygen and the concentration of bacteria arepossible, which results in a massive reduction in the requirement forreturn of highly active sludge to provide the needed concentrations ofbacteria for rapid growth. The retention time required in thebatch/continuous aeration tanks 11 needs only to be sufficient for theoxidation of the soluble matter in the wastewater. In the average case,this can be done in one to three hours, with proper control of theamount of activated sludge addition and the control of the dissolvedoxygen level.

The aeration tanks 11 receive their input flow from the second stageseparation column 10 under pressure and the maximum height of theaeration tanks 11 is determined by the liquid level and operatingpressure of the second stage pressurized air separation column 10. Thetanks 11 are operated in a batch/continuous method with the constantrate flow from the second stage separation column 10 directed to one ofthe aeration tanks 11 by control valves. The aeration tanks 11 aredesigned for a retention time of one to three hours depending on theamount of soluble material in the wastewater received from the secondstage pressurized air separation column 10. The aeration tanks 11 areequipped with a centrifugal oxygenator 3 for solid suspension and oxygentransfer at variable liquid levels. Unlike aeration tanks currently inuse, the batch process eliminates the variables of a flow-through systemand allows for control of both the bacteria concentrations and the levelof dissolved oxygen in the aeration tanks 11. The control of thebacteria concentration would be by the addition of a defined amount ofreturn activated sludge with known bacteria concentrations from thesludge storage and activation tank 20. The dissolved oxygen level in theaeration tanks 11 is controlled at a lower level as compared to currentprocess designs for aeration tanks, the purpose of which is to oxidizewastewater solids as well as soluble material. In the average case, thisdissolved oxygen level would be in the range of 2 to 4 ppm. The use ofthe centrifugal oxygenator 3 provides the ability to maintain thisdissolved oxygen level during the filling and discharge cycle of theaeration tanks 11. The discharge from each of the aeration tanks 11would be to the clarifier tanks 17 using anaeration-tank-to-clarifier-transfer-pump 12 with a valved flow ratecontrol system that would provide a constant rate of feed to theclarifier tanks 17.

Due to the small amount of solids, the low concentration of activebacteria and the controlled level of dissolved oxygen, it is possible touse a high efficiency deep liquid level settling system. Also, the useof a constant flow rate through the deep liquid level settling systemgreatly increases the separation efficiency as compared to currentlyused low liquid level variable flow clarifiers. The deep liquid levelsettling system with coil track solids conveyor is shown in more detailin FIGS. 4, 4A and 4B. The feed to the settling system (clarifier tanks)17 is provided from the batch/continuous aeration tanks 11 by theaeration tanks to clarifier transfer pump 12 using a control valve toprovide a constant flow rate. Coagulant chemicals are added from thecoagulant tanks 13 with mixer 15 by the coagulant pump 14. This flow ismade to the settling system (clarifier tanks) 17 through the inlet flowdirectional circular containment baffle 1706 which provides thecoagulant contact zone 1710. From the coagulant contact zone, thedownward flow passes into the settling zone 1712 of the clarifier tank17. The water phase then passes through the clarified water phase risezone 1708 into the overflow weir 1704 and through the clarified waterphase discharge 1714. The solids deposited into the bottom of thesettling zone 1712 are moved to the settled solids discharge 1716 by thecoil track conveyor 16. The coil track conveyor 16 consists of anelectric motor drive coil track conveyor gear reduction drive 1602, thecoil track drive shaft 1604, the coil track conveyor drive shaft bearing1606, the coil track conveyor support member 1608 and the coil track1610. The coil track conveyor action for the movement of solids iscompletely different from the solids moving equipment currently in usein wastewater treatment plants that utilize a racking or pushing actionto move the solids to a discharge point. The coil track conveyor 16applies a rotary centrifugal squeeze principle to transport the solidsacross the bottom of the settling tank to a point of discharge. Therotary centrifugal squeeze movement of solids slurry reduces the amountof solids re-suspended as compared to the raking or pushing action ofcurrently applied solids movement systems used in wastewater treatmentclarifiers.

Referring back to FIG. 1, the coagulant feed tanks 13 are vertical opentop preparation and storage tanks suitable for preparation and storageof several types of solutions of chemicals which could be used inassisting the settling of solids that were not removed in thepressurized air separation columns 7 and 10. The selection andconcentrations of the coagulant aids would be based on settling tests ineach plant. The variation in wastewater composition from system tosystem requires individual selection of the coagulant aid that will bethe most effective in assisting the settling of the solids in theclarifier tanks 17.

The coagulant feed pump 14 obtains its supply of coagulant solution fromthe coagulant feed tanks 13 and injects the solution into thepressurized pipeline transferring the wastewater from the aeration tanks11 to the clarifier tanks 17 provided with coil track conveyor 16.

The coagulant mixers 15 are standard solution mechanical drive electricmotor-driven units of suitable size to provide solution of solidmaterials in the internal reuse effluent used in the coagulant feedtanks 13.

The liquid level in the clarifier, or settling tank 17, would in almostall cases be at least double that of currently used systems. With theuse of a constant flow rate input to the clarifier tank 17 coupled withthe removal of most of the wastewater solids in the pressurized airseparation columns 7 and 10 and the control of dissolved oxygen at alltimes from the feed transferred from the aeration tanks 11, bacterialgrowth in the clarifier tanks 17 can be controlled. The retention timein the clarifier tanks 17 would be based on optimum settling timerequirements without consideration of anaerobic bacterial growth.

The sludge from the settling tanks 17 is transferred by gravity into asmall storage tank 18 which, in turn, is then transferred as needed by acentrifugal pump 19 to the slurry tank 42 feeding the dewatering system.Sludge from the settling tanks 17 needed to meet the requirements foractivated sludge in the aeration tanks 11 is stored in the sludgestorage and activation tank 20.

As the sludge underflow from the settling tank 17 has a lowconcentration of both dissolved oxygen and aerobic bacteria, it isnecessary to store the sludge in a controlled aeration tank 20 in orderto increase these concentrations to needed levels. The sludge storageand activation tank 20 is of suitable size to provide retention time tomeet the required concentration of bacteria for return to the aerationtank system. By using the centrifugal oxygenator 3 as a means of controlof the dissolved oxygen at variable liquid levels, the concentration ofthe aerobic bacteria can be maintained in the storage and activationtank 20 so that a known amount of activated sludge can be transferred tothe aeration tanks 11 to meet the requirement of the bacterial oxidationof the soluble matter in the wastewater. The return of the activatedsludge from the storage and activation tank 20 is by the use of acentrifugal pump 21 with either flow measuring equipment or a timedpumping cycle control.

The sludge transfer supply tank 18 is a vertical open top tank and wouldreceive the excess sludge flow from the bottom of the clarifier tank 17by gravity. The control of the feed of excess sludge would be based onthe requirement of the level in the sludge storage and activation tank20. The sludge transfer supply tank 18 would serve as a wetwell for thesludge transfer pump 19 and would contain a small amount of storagecapacity that would allow selection of the time cycle for transfer ofthe excess sludge to the dewatering feed slurry tank 42.

The sludge transfer pump 19 takes its suction from the sludge transfersupply tank 18 and transfers the sludge through a pipeline system to thedewatering feed slurry tank 42, as required.

The sludge storage and activation tank 20 is supplied by gravity flowfrom the bottom of the clarifier tanks 17. A liquid level control in thesludge storage and activation tank 20 would be used for control of thesludge flow from the clarifier tank 17 into the sludge storage andactivation tank 20 with all excess sludge being sent by control valvesto the sludge transfer supply tank 18. The sludge storage and activationtank 20 uses centrifugal oxygenators 3 for control of the dissolvedoxygen level in the sludge storage and activation tank 20. As a highconcentration of bacteria is needed in the activated sludge returned tothe aeration tanks 11, the dissolved oxygen level would be controlled ina normal range of 5 ppm. With a known bacterial requirement in thebatch/continuous aeration tanks 11 and a known concentration of bacteriain the sludge storage and activation tank 20, an accurate and definedreturn of the activated sludge solids can be made. Only the minimumamount of activated return sludge would be used for the necessarybacterial oxidation of the soluble matter in the wastewater.

The return activated sludge transfer pump 21 could be either acentrifugal type with flow control or flow measuring equipment or apositive displacement pump with a timed operating cycle. The pump wouldtake suction from the sludge storage and activation tank 20 and transferthe sludge through a pipeline and directional valve system to any one ofthe aeration tanks 11 as selected.

The contact columns 22 are preferred filtering media and receive theirinput flow by gravity from the overflow of the settling tanks 17. Due tothe high liquid level of the settling tanks 17, the contact columns 22operate on a gravity flow basis. The contact columns 22 consist of aflow-through support system of either perforated metal plate materialcovered with wire support screen or any other type of flow-throughsupport system that will contain the contact media and allow the liquidphase to flow through the contact area of the deep bed media and allowthe backflow of compressed air for the discharge of the spent media.

The contact media is a mixture of pulverized coal and shredded wastepaper fibers or similar waste material. The slurry is prepared in amixing tank 46 located in the fuel preparation area and transferred toeach individual contact column by a centrifugal pump 47 and pipelinesystem with control valves. The spent contact media is removed asrequired from each of the contact columns 22 through a control valvepiping system located just above the media support using the gravityflow from the settling tanks 17 and the introduction of compressed airthrough a distributor pipe located directly below the media supportsystem. The spent media slurry is discharged into a storage tank 27equipped with a mixer 28 and, in turn, is transferred, as needed, to theslurry tank 42 feeding the dewatering system by a centrifugal slurrypump 29 and pipeline system.

Unlike the currently used shallow bed sand or sand-and-coal filtersystems, the contact columns 22 would not use a water backwash systemthat in almost all cases requires a large amount of water for cleaningof the solids trapped in the media. The return of this backwash water tothe treatment system can cause a large increase in the flow-thoughdemands of the treatment plant. Also, the replacement of the media, whenrequired, can present major costs in both labor and out-of-service time.

The contact columns 22, due to the high liquid level in the clarifiertank 17, can use a media depth of from four feet to a much as fifteenfeet to meet the effluent disposal requirements of each wastewatertreatment system for the removal of solids and bacteria by attachment ofthe solid particles and bacteria to the surface of the coal and shreddedpaper fiber mixed media. As the media contains both hard particles andfiber surfaces, attachment of the small size solids that have not beenseparated in either the flotation or settling stages is much moreefficient than in the sand or sand-and-coal media systems that containonly hard particle surfaces. Removal and replacement of the media in thecontact columns does not require labor input and can be done on a fullyautomated basis without affecting the through-put flow of the wastewatersystem. Loading of media into each individual contact column 22 is doneby transfer of the coal and paper slurry from the storage preparationare by a centrifugal slurry pump 47 and pipeline system with automaticvalve control. The reused effluent used to prepare the media slurry isdischarged into the inlet of the contact column system and, in turn,returned to the chlorine contact and reuse storage tank 25. The spentmedia slurry is transferred to the slurry tank 42 feeding the dewateringsystem and only the excess water from the dewatering system is returnedto the constant rate feed an dissolved oxygen control tank 2 which, inturn, is reintroduced into the wastewater flow through the plant.

In particular the effluent contact columns 22 are vertical open topcolumns with (as shown in FIG. 5) a support system near the bottom ofthe column normally consisting of a perforated support plate 2202 and awoven metal, cloth or plastic media support member 2204. Locateddirectly below the support system is a compressed air inlet pipe system2206 for use in connection with the removal of the spent contact media.The flow throughout the contact columns 22 is by gravity based on thelevel of the discharge from the overflow of the clarifier tanks 17. Anywastewater solids not removed in the clarifier tanks 17 flow downwardlythrough a coal and paper fiber media 2208 of the contact columns 22 inwhich the solids are trapped on or in the particles of the coal ordeposited on the paper fiber. The level 2210 of the mixed media 2208 andalso the percentage of coal to paper fiber in the media would bedetermined on each installation in order to provide the most efficientoperation of the effluent contact columns 22. The diameter of theeffluent contact columns 22 would also be established by the number ofcolumns to be installed and the capacity of the wastewater treatmentplant. The loading of the media 2208 into the columns would be anindividual operation for each column using a batch process with themixed media prepared in the coal and paper fiber slurry tank with mixer46 and the centrifugal slurry pump 47 for transfer of the coal/paperslurry. The mixed media containing the correct ratio of coal and paperfiber would be prepared in the coal and paper fiber slurry tank withmixer 46 by using the feed from the paper to fiber tank with high shearmixer 45 and coal directly from the pulverized coal storage tank 38.Additions of internal reuse effluent would be used to provide properdilution of the slurry to a suitable level for pipeline transfer to aneffluent contact column 22 by way of the media inlet control valve 2226and the media inlet 2228. Additional internal reuse effluent would beused to flush the pipeline after transfer to prevent solids settling andplugging of the pipeline system. The excess flow of the internal reuseeffluent could also be used to compact the mixed media 2208 in theeffluent contact columns 22, if needed. After flowing through the mediabed, the water phase would be returned to chlorine contact and reusestorage tank 25 by gravity flow through a discharge pipeline 2212connecting the effluent contact columns 22 to the chlorine contact andreuse storage tank 25. The operation of the effluent contact columns 22would be on the basis of the differential pressure over the height ofthe media bed. High differential pressure would indicate the mixed mediabed was loaded with wastewater solids removed from the overflow of theclarifier tanks 17. When this occurs, a control valve 2214 on the columndischarge pipe 2212 is closed and a media discharge control valve 2218,in a location directly above the support system for the media, wouldopen. Compressed air would be introduced through the air inlet 2206 bythe air inlet control valve 2224 directly below the support system forthe media which, in turn, would flow upwardly at a high velocity tobreak up the compacted media bed 2208 and allow its removal by gravityflow by the effluent received from the overflow of the clarifier tanks17. The spent mixed media 2208 would flow by gravity through the mediadischarge 2216 and media discharge control valve 2218 to the spentcoal/paper reslurry tank 27. After removal of the spent media 2208, theoperational cycle would be repeated starting with the media 2208 loadingprocedure outlined above. During the period of media 2208 loading, theinlet control valve 2222 located on the column inlet 2220 would beclosed to prevent the introduction of untreated flow out of the contactcolumn 22. The number and size of the columns would be based on plantrating with a minimum of one column out of service for mediareplacement.

The gravity overflow from the clarifier tanks 17 is treated by theaddition of chlorine, or other similar chemicals, prior to itsintroduction into the contact columns 22 in order to maintain a highlevel of chlorine concentration in the contact column. The addition ofchlorine at this point terminates the growth and destroys activity ofthe aerobic bacteria which, in turn, assists in the bacterial reductionof the wastewater effluent that occurs in the coal and fiber media bed2208 of the contact columns 22.

For normal installation, a gas chlorinator 23 shown in FIG. 1 may beprovided, although other chemicals such as ozone could be used in placeof the gas chlorinator 23. The gas chlorinator 23 would be supplied withinternal reuse effluent under necessary pressure to provide solution ofthe chlorine gas into the water. The resulting solution would beinjected into the discharge pipeline of the clarifier tank 17 prior toits entrance to the effluent contact columns 22. The introduction ofchlorine at this point is for the purpose of providing assistance in thereduction of bacteria provided by the media 2208 of the effluent contactcolumns 22.

The chlorine gas supplied to the gas chlorinator 23 may be provided by,e.g., one ton or smaller pressurized storage cylinders 24.

After discharge from the contact columns 22, the effluent flows bygravity into the chlorine contact and reuse storage tank 25 (shown inmore detail in FIGS. 6 and 6A) through inlet 2510. As with the entireenergy recovery sludge free treatment process of the present invention,the height of the chlorine contact and reuse storage tank 25 wouldpreferably be more than double that currently used. The interior of thetank 25 would be equipped with flow directional baffles 2502-2508, topbaffle support plate 2514 and bottom baffle support plate 2516 thatwould prevent any short-circuiting of the flow and ensure adequateretention time for removal of excess chlorine by air stripping using acentrifugal oxygenator 3. The chlorine contact and reuse storage tank 25would be sized on the variable effluent reuse factor which would alwaysbe in excess of the time required for removal of the excess chlorinefrom the wastewater prior to its reuse in the condenser 32 and otherneeds within the treatment process system.

The internal directionalized flow baffles 2502-2508 of the chlorinecontact and reuse storage tank 25 would prevent the inlet flow fromreaching the outlet of the tank 25 without being subject to the minimumretention time required for the reduction of excess chlorine by airstripping using a centrifugal oxygenator 3. The size of the tank 25would be based on plant capacity and a minimum retention time of onehour. Underflow baffles would be used to allow the tank 25 to operate atvariable liquid levels. The chlorine contact and reuse storage tank 25would also act as a wetwell for the water reuse centrifugal pump system26 which would take its supply of water from the chlorine contact andreuse storage tank 25 as shown in FIG. 1. As the flow of the wastewatertreatment plant is a constant rate, storage is provided for the internaleffluent reuse flow to the condenser 32. Almost all of the internalreuse flow would be directed to the condenser 32 of the electric powergeneration section of the plant. Other internal uses of the effluentreuse water system would be (1) water supply to the coagulant aid system13, 15, (2) gas chlorinator system 23, (3) spent media coal/paperre-slurry tank 27, (4) coal and paper fiber slurry tank 46, (5) paper tofiber tank with high shear mixer 45, (6) ash slurry tank 55, and (7) wetscrubber system 63.

After use as cooling water in the condenser 32 of the power plantsection of the treatment plant, the internal reuse effluent is returnedfor final treatment in the effluent storage and dissolved oxygen controltank 35. Due to the possible temperature rise caused by the heattransfer of the condenser 32, adjustment of the dissolved oxygen levelsof the effluent may be required. In most cases, the use of air to reachsaturation levels of dissolved oxygen, which is sometimes required foreffluent reuse, will require many hours of retention with standardaeration devices and will not allow operation of the storage tanks atvariable liquid levels. The present invention again utilizes the abilityof the centrifugal oxygenator 3 to operate with a pure oxygen feeddirectly from storage cylinders 37 to rapidly and efficiently reach asaturation level of dissolved oxygen even under variable levels ofstorage tank operation.

Effluent storage and dissolved oxygen control tanks 35 would be ofsimilar design to the chlorine contact and reuse storage tank 25 withinternal flow directional baffles to provide maximum retention timewithout short-circuiting and would also utilize underflow internalbaffles to allow for variable level operation of the storage tank 35.The number and size of the effluent storage and dissolved oxygen controltanks 35 would be dependent on the exterior disposal requirement of thesystem. If conditions allowed the constant rate use of the effluent,only a small amount of total retention time would be required for thecontrol of the dissolved oxygen levels which would, in the average case,be less than one hour of plant through-put. Except in the case oftropical locations, the use of the exterior disposal dissolved oxygencontrol systems would only be required during summer months or periodsof high water temperature.

The effluent internal reuse supply centrifugal pump system 26 would takesuction from the chlorine contact and reuse storage tank 25 and would besized to accept the complete plant flow. The system could, in somecases, be a single unit; in the average case, due to the different flowand pressure requirements, multiple units would be needed. The balanceof the flow of the effluent internal reuse supply centrifugal pumpsystem 26, after meeting the needs of (1) the coagulant feed tanks 13,(2) gas chlorinator 23, (3) spent coal/paper re-slurry tank 27, (4)paper to fiber tank with high shear mixer 45, (5) coal and paper fiberslurry tank with mixer 46, (6) ash slurry tank 55, and (7) the wetscrubber system 63, would be sent to condenser 32 and, in turn, returnedunder pressure of the water reuse supply pump system 26 to the effluentstorage and dissolved oxygen control tank 35.

The spent coal/paper re-slurry tank 27 can be a vertical open top tanksized to retain the output of solids and liquids produced by the removalof the spent media of the effluent contact columns 22. The spentcoal/paper re-slurry tank 27 would also receive additional reuse water arequired for pipeline flushing from the internal effluent reuse supplycentrifugal pump system 26.

The spent coal/paper re-slurry tank 27 could be equipped with, e.g., anelectric driven mechanical mixer 28 of sufficient horsepower to providecomplete suspension of solids in the liquid carrier.

The spent coal/paper transfer pump 29 could be either of the centrifugalor positive displacement type dependent on the size of the plant and thedistance between the spent coal/paper re-slurry tank 27 with mixer 28and the dewatering feed slurry tank 42. The operation of the spentcoal/paper transfer pump 29 would start with the pipeline between thespent coal/paper transfer pump 29 and the dewatering feed slurry tank 42being filled with internal reuse effluent. The slurry flow from thespent coal/paper re-slurry tank 27 would be transferred on a continuousbasis, once started, to prevent pipeline plugging. In the event that theslurry transfer needed to be stopped, the spent coal/paper transfer pump29 suction would be closed off from the spent coal/paper re-slurry tank27 by a automatic control valve and receive pipeline flushing water fromthe internal effluent reuse supply centrifugal pump system 26 by asecond automatic control valve.

A package-type, factory built, low pressure steam turbine 30 providesthe drive system for an electric generators 31. The steam turbine 30 issupplied with steam by the boiler 54 which would be sized in accordancewith the capacity and pressure of the boiler 54.

A package-type, factory-built electric generator 31 is driven by thesteam turbine 30 of suitable size to match the output of the generator31.

A package-type, factory-built condenser 32, with the average size plantusing the shell and tube type, may be used to receive the dischargesteam from the turbine 30 and return the condensed boiler water to thede-aerating feed water heater 60. The sizing of the condenser 32 may bebased on the discharge conditions of the generator 31 and the allowableincrease in effluent temperature.

A package-type, factory-built condensate return tank and pump 33collects the condensate from the condenser 32 and returns the condensedboiler water to the de-aerating feed water heater 60.

To provide water protection for the steam turbine 30 and the electricgenerator 31, a building 34 may be provided having suitable size foronly these items of equipment.

The effluent storage and dissolved oxygen control tanks 35 can bevertical open top tanks with the height determined by the pressure ofthe water reuse system 26 returned from the condenser 32. The effluentstorage and dissolved oxygen control tanks 35 would be of similarconstruction to the chlorine contact and reuse storage tank 25 withdirectionalized flow baffles and underflow openings to allow forvariable liquid level operation of the tanks. To control the dissolvedoxygen levels in the tank, centrifugal oxygenators 3 would be installedin the inlet flow channel and at other points in the tank flow patternas needed for the addition of pure oxygen or enriched oxygen into theeffluent. The centrifugal oxygenators 3 would receive the oxygen supplydirectly from the oxygen storage cylinders 37 in either a gas or liquidform. The performance of the centrifugal oxygenator 3 would be improvedby the lowering of the water temperature and resulting increase inoxygen solubility that results from the lower temperature. Due to thelarge flow-through volume and the short retention time in the collectorof the centrifugal oxygenator 3 coupled with the high shear agitation,freezing or dispersion problems would not be encountered with a lowtemperature oxygen feed.

The effluent disposal centrifugal pump system 36 would be suitable forthe individual plant effluent disposal needs. As the effluent qualitywould be suitable for any type of non-potable water usage such as lawnwatering, irrigation, commercial applications or environmental reuse,the pressures required for effluent disposal would vary even in theaverage size plant. The pump would take its suction from the effluentstorage and dissolved oxygen control tank 35.

The oxygen storage cylinders 37 may be, in the case of the average sizeplant, one ton pressurized liquid oxygen cylinders of similarconstruction to the chlorine storage cylinders 24. The liquid oxygenstorage cylinders 37 would supply pure or enriched oxygen directly tothe centrifugal oxygenator 3 located in the effluent storage andissolved oxygen control tanks 35.

In order to provide the needed controlled feed of both pulverized coaland shredded waste paper material, coal and paper storage tanks 38 and39 of the vertical type with sufficient height to allow gravity feed ofthe coal and shredder waste paper are provided. The size of the storagetanks 38 and 39 would be dependent on the size of the wastewatertreatment plant and the time and cost factor of resupply caused by thelocation of the treatment plant. Both storage tanks 38 and 39 wouldnormally utilize a high density pneumatic air system for transfer ofboth the coal and paper from truck or rail cars into the top section ofthe storage tanks 38 and 39. For this reason, both of the storage tanks38 and 39 would be equipped with dust collector systems 40. For largersize plants, on-site pulverizing and shredding equipment could be used,thus allowing the use of normal coal supplies and bulk waste paper.

The feed from both the coal and paper storage tanks 38 and 39 would becontrolled by the use of rotary or similar type of solid materialfeeders 41 with dual discharges from both tanks 38 and 39. The primarydischarge from both storage tanks 38 and 39 would be into the dewateringslurry tank 43 which, in turn, would feed directly into the high densitymixer 42 located in the bottom of the dewatering slurry tank 43. Theratio of both coal and paper feed would be controlled to provide thebest possible efficiency of operation of the dewatering device 51. Thetotal amount of coal and paper feed would be determined based on eachwastewater treatment plant's wastewater solids heating value and theoverall fuel requirements of the power generation section of thewastewater treatment plant. Minimum requirements for coal and paper aredetermined by the increase in operating efficiency of the dewateringdevice 51 which is provided by the coal and shredded waste paper addeddirectly to the separated solids flow returned from the wastewatertreatment process.

The secondary feed from the coal storage tank 38 would be directed intothe coal and paper fiber slurry tank with mixer 46. The secondary feedfrom the paper storage tank 39 would be directed into the paper to fiberslurry tank with high shear mixer 45. After reduction to a fiber slurry,the slurry would be transferred by gravity to the coal and paper fiberslurry tank with mixer 46 and by the fiber slurry transfer pump 67 intothe pipeline feeding the first stage air dispersion column 5. The amountof paper fiber added would be determined to provide high efficiencyoperation of the first stage pressurized air separating column 7 and thesecond stage pressurized air separation column 10. The second feed fromthe shredded paper waste material storage tank 39 would be into thedewatering feed slurry tank 42. The second feed from the paper to fibertank with high shear mixer 45 would be by gravity into the coal andpaper fiber slurry tank with mixer 46. The ratio of coal to paper fiberadded to the coal and paper fiber slurry tank would be determined foreach plant based on the loading and the quality requirement of theeffluent disposal usage. The total amount of coal and paper placed inthe coal and paper fiber slurry tank with mixer 46 by the feeders wouldbe dependent on the media depth of the contact columns 22 found to bethe most efficient for the individual plant operation. The size of theslurry tank would be determined by the size and media depth of eachcontact column 22 and each column 22 would be reloaded with media on anindividual basis at the same time other columns 22 were in operation.Transfer of the slurry media from the coal and paper fiber slurry tankwith mixer 46 located at the storage area of the plant would be by thecentrifugal pump for transfer of coal/paper slurry 47 and a pipelinesystem with control valves to directionalize the slurry flow into thecontact column 22 selected for reloading.

The pulverized coal storage tank 38 may be of the vertical closed typewith cone-shaped bottom discharge in order to provide for gravitydischarge of the coal from the storage tank 38. The tank 38 may have astructural support base that would place the discharge of the tank 38 ata suitable level to allow gravity feed to both the dewatering feedslurry tank 42 and the coal and paper fiber slurry tank with mixer 46.The pulverized coal storage tank may be designed for high densitypneumatic loading of coal from either rail cars or truck bulk carriersThe size of the pulverized coal storage tank 38 would be dependent onthe capacity of the treatment and the ease of supply of the coal to theplant site. Also, on-site pulverization could greatly reduce the size ofthe storage tank 38.

The shredded paper waste material storage tank 39 could be of similardesign and construction to the pulverized coal storage tank 38, butnormally of larger size due to the multiple usage of the paper (a) theair separation stages, (b) the sludge dewatering stage, and (c) themixed media of the contact columns coupled with its lower bulk densityas compared to coal. As with the pulverized coal storage tank 38, ifbulk storage facilities were available, the size of the shredded paperwaste material storage tank 39 would be greatly reduced if resupply wasprovided on an on-site shredder.

Dust collector 40 of the dry type can be installed on the top of boththe pulverized coal storage tank 38 and the shredded paper wastematerial storage tank 39 to allow high density pneumatic loading of thetanks without environmental pollution.

Duplex rotary feeders 41 of the solids handling type may be installed atthe bottom of the discharge cone of both the pulverized coal storagetank 38 and the shredded paper waste material storage tank 39. Theduplex rotary feeders 41 would provide an individually controlled feedof coal into both the dewatering feed slurry tank 42 and the coal andpaper fiber slurry tank with mixer 46. The other set of duplex rotaryfeeders would provide an individually controlled feed of paper into thedewatering feed slurry tank 42 and the paper to fiber tank with highshear mixer 45. The duplex rotary feeders may be of the electric driven,variable operating speed type.

The dewatering feed slurry tank 42 may be of the rectangular closed topdesign and be located between the pulverized coal storage tank 38 andthe shredded paper waste material storage tank 39 and close enough toallow gravity flow of both coal and paper into the top of the tank 42.The dewatering feed slurry tank 42 would be placed at a verticalelevation sufficient to allow the placement of the dewatering feedslurry tank mixer 43 in the bottom section of the tank 42. In additionto receiving the gravity flow of both the coal and paper from theirstorage tanks 38 and 39, respectively, the dewatering feed slurry tank42 would receive the following slurry flows from the separation andrecycle systems of the treatment process (1) the discharge from the topof the first stage pressurized air separation column 7, (2) thedischarge from the top of the second stage pressurized air separationcolumn 10, (3) the excess settled sludge from the sludge transfer supplytank 18, (4) the return of the spent media from the spent coal/paperre-slurry tank 27, and (5) the underflow from the concentration columnfor underflow of separation columns 48. The solid material fed to theslurry tank would be coal and paper. All of these feeds would beselected and controlled to provide for efficient operation of thedewatering device and adequate fuel feed to the furnace based onelectric power demands.

As the treatment plant is operated at a constant rate of flow, changesin the input to the dewatering slurry tank 42 would be caused by achange in the composition of the wastewater entering the treatmentplant. Except in the case of an accidental dumping of material into thecollection system of the treatment plant, major changes in thecomposition of the wastewater entering the treatment plant would notoccur as long as the control of dissolved oxygen in the collection andtransmission systems is maintained. Changes in the composition of thewastewater caused by changes in sources in the collection system couldbe made without difficulty within the design basis of the energyrecovery sludge free treatment system of the present invention as longas these changes were not of the rapid cyclic type.

Current methods of dewatering wastewater solids include the use of highdegrees of centrifugal force and both high and low differential pressurefor extraction of water from wastewater solids. All other currently usedmethods are inefficient, require high power costs and have low rates ofproduction, thus requiring very high initial costs for equipment. Inmany cases, the wastewater solids are prepared for dewatering by the useof thermal systems which further increase the initial and operatingcosts of separation of the entrained water from the wastewater solids.The growth of either aerobic or anaerobic bacteria on the surface andwithin the interstructure of the wastewater solid greatly increases theretention of the liquid phase, thereby greatly increasing the problem ofdewatering of the wastewate solids.

In conventional wastewater treatment systems, the rapid growth ofbacteria on the wastewater solids is used as the primary method oftreatment of the solids. These methods of treatment result in theproduction of a biomass with high concentrations of bacteria which evenwith the most extensive treatment still contains large amounts of water,many times the weight of the solids in the biomass.

By control of the dissolved oxygen concentrations in the wastewatercollection, transmission and treatment systems, according to the presentinvention, it is possible to completely eliminate the growth ofanaerobic bacteria and to minimize the growth of aerobic bacteria. Withlow concentrations of bacteria in the separated wastewater solids, highefficiency dewatering is possible by the addition of waste paper andcoal by simply mixing the paper and coal with the wastewater solids andusing a low energy differential pressure system such as a belt presswhich provides high production rates coupled with low initial costs.

A dewatering feed slurry tank mixer 43 is provided and may be of themechanical electric driven gear reduced type with a horizontal rotatingshaft with an agitation element that would be suitable for fullsuspension and uniformity of a high density solids slurry.

A dewatering feed screw conveyor 44 may be located directly under andwould receive the discharge from the dewatering feed slurry tank mixer43. The dewatering feed screw conveyor 44 would be driven by an electricmotor through a gear reduced variable speed drive to provide the neededvariable feed rate to the continuous differential pressure dewateringdevice 51. Conveyor systems suitable for transfer of high density slurryother than a screw conveyor can be used for this application.

A paper to fiber tank with high shear mixer 45 may be of the open topvertical type and would receive a supply of internal reuse effluent fromthe water reuse supply centrifugal pump system 26 and its feed ofshredder paper directly from the shredded paper waste material storagetank 39. The high shear mixer can be used to prepare a supply of paperfiber slurry for use by both the fiber slurry transfer pump 67 and thecoal and paper fiber slurry tank with mixer 46. The paper fiber slurryprepared in the paper to fiber tank with high shear mixer 45 would befed by gravity into the coal and paper fiber slurry tank with mixer 46where the addition of coal would complete the preparation of the mixedmedia for the effluent contact columns 22. A single split tank designcould be used to combine the operation of both the paper to fiber tankwith high shear mixer 45 and the coal and paper fiber slurry with mixer46 into a single unit with the high shear mixer affecting only one-halfof the tank contents and the second slurry suspension mixer affectingthe second one-half of the tank contents for suspension of the coal andfiber mixed media for the contact columns 22. The reduction of theshredded paper waste material would be on a continuous preparation basisas a continuous supply of the paper fiber is required for the additionto the pipeline prior to the first stage air dispersion column 5. Theamount of fiber necessary for the efficient operation of the first stagepressurized air separation column 7 and the second stage pressurized airseparation column 10 is dependent on the concentration of wastewatersolids, the capacity of the plant, the amount of bacterial developmenton the surface of the solids and the needed efficiency of removal of thewastewater solids by the pressurized air flotation stage of the process.The fiber requirements, depending on conditions, could be as little as10% by weight of the solids removed to as much as a equal weight offiber for weight of the solids removed in the pressurized air flotationstage of the process. The fiber slurry transfer pump 67 would providethe controlled addition of the fiber slurry to the pipeline injectionpoint located near the first stage air dispersion column 5.

The coal and paper fiber slurry tank with mixer 46 could be either anindividual vertical open top tank or a split tank with one side of thetank used for the paper to fiber tank with high shear mixer 45, and theother side for the coal and paper fiber tank with mixer 46. As the paperto fiber tank with high shear mixer 45 must be operated on a continuousbasis, the slurry level in the tank would be maintained at a highconstant level. This requirement allows for the gravity flow of theprepared fiber slurry for the paper to fiber tank with high shear mixer45 into the coal and paper fiber slurry tank with mixer 46 by gravity.As the operation of the coal and paper fiber slurry tank with mixer 46is only required when the replacement of the media is needed in one ofthe contact columns 22, on the average it would only be used one tothree times in a twenty-four hour plant operating cycle. The coal andpaper fiber slurry tank with mixer 46 would be supplied with twoadditions other than the fiber slurry from the paper to fiber tank withhigh shear mixer 45. The addition of coal needed for the mixed mediawould be directly from the pulverized coal storage tank 38. The effluentrequired for the slurry preparation would be supplied by the internaleffluent reuse system 26. The mixed media would be transferred by thecentrifugal slurry pump 47 to the contact column 22.

The centrifugal slurry pump 47 for transfer of the coal and paper fiberslurry would obtain its suction from the coal and paper fiber slurrytank with mixer 46. The centrifugal slurry pump for transfer of coal andpaper fiber slurry 47 would transfer the slurry through a pipelinesystem with automatic control valves located at each of the effluentcontact columns 22 in order to load the media into the column. When theneeded amount of media slurry has been transferred from the coal andpaper fiber slurry tank with mixer 46 to the contact columns 22, reusewater would be added to the tank and, in turn, to the suction of thecentrifugal slurry pump 47 for transfer of coal and paper fiber slurryin order to flush the pipeline system and prevent plugging of the systemwith media solids.

A concentration column 48 for underflow of separation columns is avertical pressurized tank having (as shown in FIGS. 7 and 7A) an inlet4802 located in the top head 4818 and an inlet directional flow circularbaffle 4812 which directs the flow downward in the center section of thecolumn to provide directional settling of the high density solids. Fromthe inlet directional flow circular baffle 4812, the flow enters thesettling zone 4814 with the solids concentrated in the center of thebottom head 4820. The water phase flows upward through the raise zone4816 and is collected by the outlet collection weir 4822 and, in turn,is discharged through the outlet 4804 to the constant rate feed anddissolved oxygen control tanks 2 by way of the control valve 4806. Thehigh density solid slurry is removed through the settled solids slurrydischarge 4808 by way of the control valve 4810 using the internalpressure of the column and fed into the dewatering feed slurry tank 42.

Since compressed air is not used for biological oxidation of wastewatersolids, but only for dissolved oxygen control, media suspension,operation of control valves and supply to air dispersers, only a smallamount is required when compared to other processes. As the air pressurerequired in most systems will exceed 25 psi, a centrifugal compressorand air storage tank system is utilized for overall plant air supply.

Referring back to FIG. 1, a compressed air storage tank 49 may beprovided as a closed pressurized tank of either the vertical orhorizontal type. The size and operating pressure would be determined bythe air requirements of the plant based on its capacity. The use of theair storage provides for efficient operation due to the variable times,rates and pressures required in the process of the present invention.

A centrifugal air compressor 50 may provide the supply of compressed airto the compressed air storage tank 49. The use of the centrifugal aircompressor type unit 50 provides the column and pressure required forthe operation of all of the air demand systems which have widely varyingair pressure requirements.

A continuous differential pressure dewatering device 51 receives itsfeed of high density slurry from the dewatering feed slurry tank 42 byway of the dewatering feed screw conveyor 44. A belt press or similartype of unit would be the normal selection of the equipment used toremove the excess water from the slurry of coal, paper and wastewatersolids. The dewatering unit could use either pressure or vacuum as thesource of the required differential pressure. The dewatered solids wouldbe discharged from the continuous differential dewatering device intoeither a fluidized bed or a travelling grate furnace 53 and the excesswater could be transferred by a centrifugal pump 52 to the constant ratefeed and dissolved oxygen control tanks 2.

A travelling grate 53 or fluid bed furnace would be the normal selectionfor the combustion of the coal, paper and wastewater solids dischargedfrom the continuous differential pressure dewatering device 51. Thesizing of the travelling grate 53 or fluid bed furnace would bedependent on the capacity and concentration of solids in the wastewateras a minimum, but larger size units could be used based on the marketfor excess electrical power and the cost and availability of waste paperand coal.

Because the system operates at constant low rates, the electricalrequirements of plant operation are almost constant during a 24-houroperating cycle which, in turn, would allow the storage of high densityslurry for use as fuel for peak operation of the furnace and boilersystems to supply excess electric power to utilities for assisting inthe supply of electrical power during their peak load cycle.

A factory-built, package-type boiler 54 matched to the size of either afluidized bed or a travelling grate furnace 53 would be used in smalland average size plants for the conversion of the combustion energyproduced by the travelling grate 53 or fluid bed furnace into steam foroperation of the steam turbine 30. Large size treatment plants mayrequire field erected size boiler units 54. For very large plants,efficient increasing devices such as an air preheater may be added tothe system.

The ash generated by the travelling grate 53 or fluid bed furnace may bedischarged into a vertical top slurry tank 55 and mixed with internalreuse effluent from the internal effluent reuse supply centrifugal pumpsystem 26, the underflow from the wet scrubber system 63 and the decantpump 59 returned from the ash storage and decant tank 58.

The ash slurry tank 55 may be equipped with an electrically drivenmechanical mixer 56 of suitable size to provide full suspension of thesolids in the water phase.

An ash slurry transfer pump 57 may take its suction from the ash slurrytank 55 and transfer the slurry through a pipeline system to the ashstorage and decant tank 58 on a continuous basis.

The ash storage and decant tank 58 may be a vertical elevated open toptank with a cone-shaped bottom for settling and storage of the solidsremoved from the slurry transferred from the ash slurry tank 55. Theelevation of the tank 55 would be determined by the method used for ashdisposal.

A decant pump 59 may remove the excess water from the ash storage anddecant tank 58 and transfer it to the ash slurry tank 55. The ash fromthe storage tank 58 may be removed by gravity flow into a track or railcar for land fill disposal.

A package-type, factory-built de-aerating feed water heater 60 ofsuitable size for the boiler 54 may be used to store and heat the boilerfeed water returned from the condenser 32 and additional treated waterfrom the boiler water treatment demineralizer system 62. The steamrequirements for the de-aerating feed water heater 60 may be suppliedfrom the exhaust of the steam turbine 30.

A boiler feed pump 61 may take its suction from the de-aerating feedwater heater 60 and inject it into the boiler 54.

The boiler water treatment demineralizer system 62 may be afactory-built unit of suitable production capacity for the size of theboiler 54 and may be supplied with potable water for treatment to meetthe quality standards of the boiler 54.

A factory-built, package-type wet scrubber system 63 may be used foremission control of the exhaust of the travelling grate furnace 53 usingwater supplied by the water reuse supply centrifugal pump system 26. Theunderflow of the wet scrubber system 63 would be discharged by gravityinto the ash slurry tank 56.

A centrifugal exhaust fan 64 ma be used for air flow through thetravelling grate furnace 53 if used. For the use of a fluid bed furnace,the centrifugal fan 64 would be used for fuel suspension. A wet scrubbersystem 63 and the discharge stack 65 can be provided for either furnacesystem.

An exhaust discharge stack 65 of suitable size and height may be usedfor discharge of the air flow from the centrifugal exhaust fan 64.

An air preheater 66 ma be used to transfer the thermal energy of thefurnace exhaust to the incoming air fed to the furnace combustionchamber.

A fiber slurry transfer pump 67 may be used for the supply of fiberslurry from the paper to fiber tank with high shear mixer 45 to thepipeline injection point located just prior to the inlet of the firststage air dispersion column 5.

While I have shown and described several embodiments in accordance withthe present invention, it is understood that the same is not limitedthereto, but is susceptible to numerous changes and modifications asknown to a person having ordinary skill in the art, and I therefor donot wish to be limited to the details shown and described herein, butintend to cover all such modifications as are encompassed by the scopeof the appended claims.

I claim:
 1. A process for treating wastewater containing insoluble solidwaste material and soluble solid waste material comprising the followingseries of steps:controlling the oxygen content of said wastewater to alevel at which growth of anaerobic bacteria is substantially eliminatedand growth of aerobic bacteria is minimized; separating said insolublesolid waste material from said wastewater; treating said soluble solidmaterial in said wastewater with a predetermined amount of aerobicbacteria; and reducing the amount of aerobic bacteria in saidwastewater.
 2. A process according to claim 1, wherein said oxygencontent is in the range of 0.5 to 1.0 parts per million.
 3. A processaccording to claim 1, wherein said insoluble solid waste material isseparated from said wastewater by mixing said wastewater with paperfiber, dispersing a gas in said wastewater and allowing the wastewatercontaining paper fiber and dispersed air to flow upwards through asubstantially vertical column, whereby insoluble solid waste materialhaving a higher settling rate is collected at a bottom of said columnand separated from said wastewater and insoluble solid waste having alower settling rate attaches to rising gas bubbles and is collected atan upper part of said column and separated from said wastewater.
 4. Aprocess according to claim 3, wherein said gas is air.
 5. A processaccording to claim 3, wherein said upper part of said column is under apressure greater than atmospheric pressure.
 6. A process according toclaim 3, further comprising a steep of burning the insoluble solid wastematerial and said paper fiber separated from said wastewater.
 7. Aprocess according to claim 1, wherein the step of treating said solublesolid material comprises adding sludge having a predeterminedconcentration of aerobic bacteria to said wastewater.
 8. A processaccording to claim 1, further comprising, after the step of treatingsaid soluble solid material, a step of flowing said wastewater through afiltering medium to trap solid waste material not previously separatedfrom said wastewater.
 9. A process according to claim 8, wherein thestep of reducing the amount of aerobic bacteria in said wastewateroccurs before said step of flowing said wastewater through a filteringmedium.
 10. A process according to claim 9, wherein the step of reducingthe amount of aerobic bacteria in said wastewater comprises contactingsaid wastewater with a predetermined amount of chlorine, and whereinsaid filtering medium is a coal and paper fiber medium.
 11. A processaccording to claim 10, further comprising removing said coal and paperfiber medium and burning the removed coal and paper fiber medium and theinsoluble solid waste material separated from said wastewater.
 12. Aprocess according to claim 1, further comprising a step of burning theinsoluble solid waste material separated from said wastewater.
 13. Aprocess according to claim 1, further comprising, after the step ofreducing the amount of aerobic bacteria in said wastewater, a step ofdissolving oxygen in said wastewater and then disposing of saidwastewater.